Gearshift transmissions of motor vehicles are usually controlled or shifted by means of an actuating device arranged within reach of the driver. As a rule actuating elements such as a gearshift lever or selector lever are used for this, which are arranged for example between the front seats of the motor vehicle.
The design and ergonomic requirements for such actuating devices or selector levers for gearshift transmissions are many and various. For example, to enable the driver for reasons of safety and ergonomics to have a realistic feeling of transmission actuation, actuating devices of this type are required to provide the driver with both visual and clear haptic or tactile feedback. From this the driver should be able to conclude, when operating the selector lever, which shift process has actually taken place in the transmission. Likewise, it should be possible for the driver to grasp intuitively the shift condition of the transmission at the time, with a glance or by touching the selector lever.
It is therefore desirable to communicate to the driver clear visual and tactile feedback about the current transmission condition or the actual gear engaged, with reference to the position or angular setting of the selector lever at the time.
In the case of mechanical transmission actuation or a mechanical link between the selector lever and the gearshift transmission—for example by means of a cable pull or link-rods—the selector lever position always corresponds to the actual transmission setting because of the mechanical coupling. Since mechanically actuated gearshift transmissions are generally multi-stable (the transmission shift setting is stable in several or all positions, so it does not change spontaneously), the associated selector lever is also multi-stable and therefore, like the gearshift transmission itself, remains in the respective position or gear engaged by the driver.
Consequently the driver can on the one hand conclude from the selector lever position at the time what the current shift condition of the transmission is, or, with reference to the selector lever position, he can recognize the gear engaged in the transmission, and can on the other hand rely on the fact that the selector lever position is not misrepresenting the shift condition of the transmission.
However, in the case of the increasingly used electric actuation or so-termed shift-by-wire actuation of gearshift transmissions, there is no longer any mechanical link between the actuating element or selector lever in the passenger compartment and the transmission of the motor vehicle in the engine compartment. Rather, in the case of transmissions controlled by the “shift-by-wire” method, shift commands are transmitted from the actuating device to the transmission of the motor vehicle mostly exclusively by means of electric or electronic signals and are implemented by subsequent, mostly electro-hydraulic conversion of the shift commands. This applies in part as well to modern change-speed or gearshift transmissions, but in particular to the current generations of automatic transmissions, which are mostly actuated completely remotely by actuators.
In the case of gearshift transmissions actuated “by-wire”, however, the lack of a mechanical connection between the transmission actuating system and the selector lever can cause the selector lever position, under certain boundary conditions or in the event of a fault, no longer to correspond to the actual shift condition of the transmission.
For example, modern automatic transmissions generally comprise a so-termed Auto-P function, which ensures that when the vehicle is left, if necessary the parking lock is automatically engaged in the transmission, so as perhaps to prevent the unattended vehicle from rolling away if the driver has forgotten to engage the parking lock before leaving the vehicle. In other words the Auto-P function, which comes into action automatically in particular when the ignition key is withdrawn or when the vehicle is left, ensures that the parking lock is engaged automatically in the transmission regardless of the drive position actually selected with the selector lever. Thus, the parking lock is engaged by the Auto-P function of the transmission or the vehicle when the selector lever has been left by the driver, for example in the neutral position, in a manual-shift gate if there is one, or in one of the gear positions.
In such a case, however, the position of the selector lever no longer corresponds with the actual shift condition of the transmission. Accordingly, when the driver returns to the vehicle or attempts to start it, by virtue of the selector lever's position the driver to begin with receives incorrect information both visually and by touch. On the basis of his perception of the selector lever position the driver would thus assume, for example, that the transmission is in its neutral position or in a particular gear, whereas in reality the parking lock is engaged in the transmission. This discrepancy between the selector lever position and the condition of the transmission could therefore lead to undesired erroneous operations, wrong conclusions by the driver, and thus also to safety-critical situations. To prevent this a specific, additional signal device for the driver must be provided, which alerts him to the fact that the parking lock has been engaged by Auto-P and that the vehicle can only be started when the selector lever has first been put manually in the parking lock position and thus brought into correspondence with the actual shift status of the transmission.
It has been sought to overcome the above problem by designing the selector levers of shift-by-wire gearshift transmissions as mono-stable actuating elements. In other words, this means that such a mono-stable selector lever, after each actuation, always returns again to the same central position. With a mono-stable selector lever, the feedback on the actual shift status of the transmission therefore relies exclusively on a separate display, for example by means of light-emitting-diodes. On the other hand, with a mono-stable selector lever there is no possibility of providing the driver with visual or tactile feedback about the shift status of the transmission. Moreover, implementation of the mechanical shift logic and the necessary locks—such as the so-termed Keylock and Shiftlock lock systems—in the case of mono-stable selector levers is usually difficult and demands elaborate actuator means for the selective blocking of inadmissible shift commands as a function of the driving status of the motor vehicle, which entails complex design and correspondingly high costs.
For example, the safety function known as the Keylock system, in the case of automatic transmissions, results in a blocking of the selector lever in the “P” position so long as the ignition key is withdrawn.
With actuating devices having a mechanical link to the gearshift transmission, this accordingly prevents unintentional actuation of the selector lever when the ignition key has been withdrawn or when the ignition is switched off, which could result in unintentional disengagement of the parking lock, allowing the vehicle to start moving when this is not desired.
Another example of such a safety function that can only be implemented in the case of mono-stable selector levers with comparatively great effort is the Shiftlock lock system, which serves to ensure that for safety reasons, it is only possible to shift out of the positions “P” and “N” when the brakes are applied. This also serves the purpose of preventing uncontrolled starting-off of the vehicle already at the moment when a gear is engaged.
The known, mono-stable actuating devices also have the disadvantage that the driver has to become accustomed to a new operating concept since the lever always tends to return to its central position, this operating concept being considerably different from the traditional transmission actuation mode.